The invention is directed to the production of vicinal diols, thus diols whose hydroxyl groups are on adjacent carbon atoms, by saponification of the corresponding epoxide.
Vicinal diols hve numerous uses, e.g., as intermediate products in the production of butadiene and isoprene, which are formed from the corresponding diols by dehydration.
Additionally, they play a role as components in the production of polyesters and polyurethanes, as well as in the cosmetic and pharmaceutical industries.
Vicinal diols are produced, among other procedures, by saponification of the corresponding epoxide. Thereby, this saponification is catalyzed both by the addition of acids (see, e.g., the state of the art of U.S. Pat. No. 3,576,890), as well as alkalis (see, e.g., German OS No. 1793247, German OS No. 2203806), as well as salts of aliphatic mono or polycarboxylic acids (German OS No. 2256907), as well as primary, second, or tertiary amine salts or ammonium salts (European published application No. 0025961).
It is also known to produce the acids functioning as catalysts by the addition of esters of lower carboxylic acids and hydrolysis of the esters of alcohols and acids (U.S. Pat. No. 3,576,890).
The saponification can be carried out in pure aqueous medium or in the presence of solvents such as water soluble ketones or cyclic ethers (German OS No. 2256907).
The saponification is carried out not only directly with the epoxides, but it is also possible to form first, e.g., a lower carboxylic acid ester, which then is saponified (J. Amer.Chem.Soc., volume 66, page 1925 (1944). This process is used for the most part with long chain epoxides.
In addition to the yield of diols, the selectivity is also important. The latter is influenced by holding the pH, which is in the weakly acid region, as constant as possible. For this purpose, processes were developed which operate in the presence of carbon dioxide (see U.S. Pat. No. 2,623,909 and German OS No. 2,615,595). Thereby, there must be employed a discontinuous operation in an autoclave under increased pressure, which is in part considerably high, see the examples cited therein.
According to the state of the art in the first line there were saponified either lower epoxides such as ethylene oxide or propylene oxide or higher epoxides having, e.g., 12 to 18 carbon atoms, to the corresponding vicinal diols.
If in this process the general range is given for the number of carbon atoms of the epoxide, which in the lower epoxides goes up to about C.sub.5 and in the higher epoxides goes down to about C.sub.4, then there is used in the examples ethylene oxide or propylene oxide or higher epoxides with, e.g., 12 to 18 carbon atoms.
The intermediate range of isomeric pentene oxides to heptene oxides in their direct saponification to the corresponding diols, previously has not led to industrial realization.
However, precisely the diols of this intermediate range are essential in the production of, e.g., pesticides.
Therefore, the task of the present invention is the direct saponification of epoxides having 3 to 8, preferably 5 to 7, carbon atoms of the corresponding vicinal diols in good yields and with high selectivity.